A bit of ear goop can reveal if sheep are eating dangerously poisonous plants.
Earwax from sheep that have eaten death camas contains the plants’ toxins within a few days following the noxious meal, researchers report in the December 2024 Toxicon. The findings add to a growing list of medical insights researchers can glean from swabbing some wax (SN: 2/24/14).
While grazing in pastureland, livestock like cattle and sheep can die from eating poisonous plants. Determining the culprit is a big job, says Stephen Lee, an analytical chemist at the U.S. Department of Agriculture’s Poisonous Plant Research Lab in Logan, Utah. Lab workers might visit the pasture to test plants or analyze blood from living herd members, which requires specialized training and equipment. Lee and his colleagues have been studying earwax as a simpler sample that can indicate if animals are being exposed to fatal forage.
The team focused on death camas (Zigadenus paniculatus, sometimes classified as Toxicoscordion paniculatum), a relative of lilies that grows in much of the western U.S. Livestock that eat enough of the plants suffer from the toxic effects of two compounds, zygacine and zygadenine, which cause mouth frothing, teeth grinding, twitching, stiff-legged walking, vomiting and potentially death, often via heart and respiratory failure. Lee and his team knew from previous studies that there was a death camas dosage that could be given to the sheep to make them sick, but not severely ill to the point of death. So, the researchers dosed sheep with just enough of the toxic compounds by infusing an alfalfa slurry with an extract from death camas. The researchers then took earwax samples every few days for month, starting on day three. They also sampled earwax from sheep that grazed in a pasture chock full of death camas for three days.
The researchers detected the toxins in the earwax of the dosed sheep, with concentrations highest three days after eating the spiked alfalfa and decreasing over the following weeks. Earwax from all of the sheep that grazed in the pasture with death camas also tested positive. Lee thinks that similarly to how certain chemicals and drugs can be deposited in humans and animals’ hair and sweat after they’re consumed, the wax glands in the ear secrete some of the plant toxins.
The findings add to the team’s previous research showing toxins from different poisonous plants can turn up in cattle earwax. Earwax may be a useful tool for ranchers to quickly locate toxic plants—even pinpointing them to a specific pasture by analyzing the grazing habits of affected animals—and protect their livestock.
“If these animals are out on the range, they are free-choice eating, and most of the time they’re not being watched very closely,” says Lee, so poisoning prevention is key.
Researchers are increasingly recognizing earwax as a sticky window into health, though much of this research has focused on humans. Our earwax may show markers of diabetes, cortisol levels, metabolic changes and even cancer.
Lee and his team’s approach might someday be adapted to detect certain drugs — like morphine and codeine — in humans, says João Barbosa, a chemist at Örebro University in Sweden. Such drugs are broadly chemically similar to zygacine and zygadenine.
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